The traditional approach of conducting communication with an implantable medical device (IMD) has been through use of inductive telemetry. Currently, the inductive telemetry is replaced by radio frequency (RF) based communication protocols. Usage of RF carriers provides longer communication distances but also introduces new challenges when designing an IMD and its communication circuitry.
One such challenge is that the RF receivers of the IMD should be able to operate within a band of radio frequencies. Broadband RF receivers having optimal receiver frequency within the whole band of radio frequencies are today not practically feasible for IMDs. In clear contrast, practical broadband RF receivers for IMDs generally have varying receiver sensitivities at different radio frequencies within the RF band. A transmitter of a non-implantable communication device can then send at any radio frequency in the band with the potential consequence of the broadband RF receiver missing the communication attempt if the reception condition is poor and the transmission was on a mismatched radio frequency where the broadband RF receiver performs less optimally.
U.S. Pat. No. 7,065,409 discloses an external unit that learns the transmit and receive frequencies for an IMD. The transmit frequency of the IMD is learned by the external unit measuring a difference between the transmit frequency of the IMD and the receive frequency of the external unit. The receive frequency of the IMD is learned by the measured difference between the transmit frequency of the IMD and the receive frequency of the external unit when the implant has a fixed transmit and receive frequency difference. Otherwise, the receive frequency is learned by the IMD measuring the difference between its receive frequency and the transmit frequency of the external unit and by sending an indication of the difference to the external unit through a return signal.
There is, however, still a need for improvements in connection to RF-based communication between an IMD and a non-implantable medical device.